1. Field of the Invention
This invention relates to laser sources used in optical drives, and more particularly, to a two-wavelength laser diode package that can be utilized in the read/write head of an optical drive, allowing the optical drive to be capable of reading data from two different types of optical discs, such as CD (compact disc), CD-R (CD Recordable), and DVD (digital versatile disc).
2. Description of Related Art
A laser diode is a semiconductor laser source which is capable of generating a laser beam of a specific wavelength. The laser diode is useful in many various applications; for example, it can be used in an optical drive for reading data from an optical disc, such as a CD, a CD-R or a DVD. Laser diodes are usually supplied in packages. Conventional laser diode packages, such as the widely used TO type package, are structured to pack only a single laser diode therein that allows the laser diode package to be useful for generating a single-wavelength laser beam. In some applications, however, two different wavelengths of laser beams may be required, such as an optical drive capable of reading data from two different types of optical discs.
FIG. 1A is a schematic perspective diagram showing a conventional laser diode package which packs one single-wavelength laser diode therein; and FIG. 1B shows a variation to the inside structure of the laser diode package of FIG. 1A.
As shown in FIG. 1A, the laser diode package includes an enclosure 18 which is used to pack a laser-diode chip 10, a submount 12, a heat sink 14, and a power monitor 16 therein. Inside the enclosure 18, the laser-diode chip 10 is mounted on the submount 12, and the submount 12 is mounted on the heat sink 14 which is used to dissipate the heat generated from the laser-diode chip 10. Further, the enclosure 18 is formed with a window 20 on the top thereof which allows the laser beam generated by the laser-diode chip 10 to pass therethrough to the outside of the laser diode package.
FIG. 1B shows a variation to the inside structure of the laser diode package of FIG. 1A, in which the power monitor (here designated instead by the reference numeral 16a) is mounted along with the laser diode (here designated instead by the reference numeral 10a) on the submount (here designated instead by the reference numeral 12a). Fundamentally, the power monitor should be disposed on the back side of the laser-diode chip for the purpose of monitoring the output power of the laser beam generated by the laser-diode chip.
The foregoing laser diode package is only capable of providing a single-wavelength laser beam that can be used in an optical drive to read data from one type of optical disc, such as the conventional low-density CDs or CD-Rs. With the advent of new high-density optical storage media, such as the newly introduced DVDs, a laser beam of a shorter wavelength should be used to read data from this new type of optical disc. For compatibility reasons, however, new DVD drives should be also capable of reading data from the old type of optical discs (i.e., CDs or CD-Rs) so that their use is more versatile.
FIG. 2 is a schematic diagram showing the optical structure of the read head of an optical drive that is capable of reading data from either a CD, a CD-R or a DVD. As shown, this read head includes a pair of separate single-wavelength laser sources including a first laser source 22a (a laser module including a laser diode and a photo-detector) for generating a laser beam of a first wavelength, for example 780 nm (namometer), and a second laser source 22b (a laser diode) for generating a laser beam of a second wave-length, for example from 635 nm to 650 nm. The first and second laser sources 22a, 22b can be selectively activated depending on the type of the optical disc (for example, a CD, CD-R or a DVD) currently being inserted in the drive. In the case of reading a CD or a CD-R, for example, the first laser source 22a is activated while the second laser source 22b is deactivated; whereas in the case of reading a DVD, the first laser source 22a is deactivated while the second laser source 22b is activated.
When the first laser source 22a is activated (in the case of reading a CD or a CD-R, for example), it generates a laser beam which is then reflected by the reflective mirror 24a to an object lens 26a where the laser beam is focused onto the CD or CD-R where the data to be read out are located.
When the second laser source 22b is activated (in the case of reading a DVD, for example), it generates a laser beam which is then reflected by a beam splitter 24b to another propagation path 20b and subsequently passes through a collimator 28b where the laser beam is collimated into a straight beam. Subsequently, the laser beam passing through the collimator 28b is reflected by a reflecting mirror 30b to an object lens 32b where the laser beam is focused onto the DVD where the data to be read out are located. The reflected light from the DVD then propagates reversely back to the beam splitter 24b which admits part of the reflected light to transmit therethrough to a propagation path 20c on which a photo detector 26b is mounted.
One drawback to the foregoing read/write head has the complexity in structure. A CD-R can only access data by using a laser light of 780 nm. To achieve the reverse compatibility of CD-R, the high manufacturing cost is high since two separate single-wavelength laser sources, for example, one laser diode of 635 nm to 650 nm and the other laser of 780 nm, are required to allow the optical drive to be able to read data from either a CD, a CD-R or a DVD. With the advent of the high-density DVDs, newly developed optical drives are specifically designed to read data from this new type of optical disc. For compatibility reasons, however, new DVD drives should be also capable of reading data from the old CDs or CD-Rs so that the customers can have more versatility in using their new optical drives. There exists, therefore, a need for a laser diode package that can be used to selectively generate one of two laser beams of different specifications in wavelength.